The modern concept of biological sensors evolved considerably over the forty years since it was first demonstrated that enzymes could be immobilized at a surface of an electrochemical detector. Demands to reduce the sample volume, the cost and the time of analysis, and to increase sensitivity and selectivity have been most pressing in biological and biomedical sciences. This has fueled development of micro-analytical devices and bio-sensors with a wide range of applications in the clinical and defense settings, in gene and forensic analysis, in environmental monitoring, food safety and many other settings. While selectivity of biological sensors always derives from the unique molecular recognition interactions, such as antibody-antigen binding or complimentary deoxyribonucleic acid (DNA) hybridization, transduction and amplification of these events into analytically useful signal is often a major challenge.
Interest in detecting DNA in a sequence-specific manner has grown steadily in recent years. The ability to rapidly and inexpensively detect DNA of specific sequences may allow more efficient pathogen, point mutation and gene detection. Multiple approaches of detecting DNA in a sequence-specific fashion have been explored, including optical (for example, chemiluminescence fluorescence, Raman spectroscopic and surface plasmon resonance), electronic as well as numerous electrochemical methods. Historically, fluorescence methods have been the most sensitive. However, advances in the electrochemical detection of DNA are becoming competitive in terms of sensitivity.
Detection of pathogenic species in water is also an important and challenging problem. Several examples reporting direct response sensor devices sensitive to bacteria, viruses and bacterial toxins exist. These include, for example, colorimetric sensors designed to detect influenza virus and E. Coli and an electrochemical sensor responding to E. Coli enterotoxin.
These technologies, however, have certain disadvantages. It is therefore desirable to provide improved methods and apparatus for electrochemical sensing of a target substance. In one example, it is desirable to provide sensors having microfabrication efficiencies that are highly accurate and yet inexpensive enough so that they are disposable.